1. Field of the Invention
The present invention pertains to apparatus for mixing liquid and pulverulent materials, and in particular, to automatic mixing systems.
2. Description of the Related Art
Paint shakers and other apparatus for mixing paint and the like products in a sealed container have been in wide spread use for some time. One common use for such apparatus is to mix paint products in familiar standardized containers such as quart and gallon sized cans and five gallon plastic pails. Oftentimes, paint is mixed at a store location, one container at a time. After adding colorants and other ingredients, the container is put into a shaker machine for thorough mixing of the ingredients.
However, paint and paint products are also prepared commercially, on a much larger scale, with large numbers of containers being pelletized for shipment to remote locations. At times, pallets of paint containers are stacked one on top of another, with considerable pressure being applied to the lower most row of containers on the bottom pallet. Even if the bottom containers are not ruptured, they may become seriously weakened and may even be partly crushed.
Paint shakers impart a considerable force to a container and its contents, and the container is moved back and forth in a series of short, rapid movements. It is important that the paint container be securely held in the shaker machine. In some paint shaker machines, a band is clamped about the girth or circumference of a paint can, or a series of small clamps are spaced about the periphery of the can lid. Such clamping arrangements, which are typically employed for mixing quart or gallon-sized cylindrical containers, are unsuitable for use with five gallon containers which typically are tapered from top to bottom. Because of the size, weight and asymmetric nature of five gallon containers, it is usually expedient to clamp such containers in an upright position, between a pair of horizontal clamp members. Such clamping arrangements, if made of larger size clamping plates, may also be employed to shake several containers, simultaneously. Five gallon containers of paint products, especially those with masonry fillers are quite heavy, weighing up to 70 pounds or more. A substantial clamping force is required to retain such containers during a mixing or shaking operation and, under normal conditions, adequate clamping force can be achieved without risk of damage to the paint container. However, damaged paint containers, such as those weakened during shipment, prior to a mixing operation, present an abnormal condition which may not be detected upon their loading in a paint shaker machine. Such abnormal containers may even rupture during mixing operation, if care is not taken when clamped in the shaker machine.
With present shaker machines it is not always possible to adequately clamp such weakened containers with pressure sufficient to adequately retain the container during mixing, while limiting the pressure so as not to aggravate the previously compromised integrity of the container. A clamping arrangement which is reliable and easy to use, and which offers a greater precision in the application of pressure to a container is still being sought.
Paint and paint formulations are a worldwide industry and with increasing frequency, larger paint handling operations are encountering different-sized containers, with an increasing number of containers being of an unusual size or proportion and not constructed according to domestic or foreign standardized dimensions. It is important that the paint shaker be readily adaptable to such containers. Further, in the manufacturing environment, it is important that the paint mixers be capable of rapid operation in loading and unloading containers therefrom.